ON A NEW ORGAN IN THE LYCORIDEA. 397 



The nephridium may, therefore, be described as a mass of 

 conuective tissue, iu which is embedded an excretory canal, 

 the wall of which has a small number of nuclei in it, but no 

 distinct cell outlines. 



It is well known that Ehlers (5) described the nephridium 

 of N. cultrifera as having a long duct leading to the exterior, 

 and a crescent-shaped internal opening. Schroder (9), who 

 seems to have copied Ehlers' errors as carefully as his correct 

 observations, gives a similar figure and description of the 

 nephridium in N. diversicolor. I feel convinced that these 

 observers, examining the nephridium after its removal from 

 the worm, have simply mistaken the post-septal canal for the 

 duct to the exterior, and that their internal opening is the 

 scar left on tearing the organ away from its attachment to the 

 body-wall at the nephridiopore. This interpretation is con- 

 firmed by the fact that Ehlers states that " die Richtung der 

 Flimmerbewegung ging an der ausseren Miindung nach 



Summary and Conclusions. 



We may sum up the main facts set forth above as follows : 

 Nereis diversicolor has in every segment, except the 

 first and last few, a pair of large, highly differentiated, ciliated 

 patches of coelomic epithelium — the dorsal ciliated organs. 

 These organs seem to occur throughout the Lycoridea, as they 

 have been found in all the genera of that family which I have 

 examined. 



The nephridium of Nereis diversicolor consists of a 

 compact mass, perforated by a convoluted canal, which can be 

 distinguished into several regions, and communicating with the 

 exterior by a short duct leading to a nephridiopore on the 

 ventral surface. A long canal springs from the main body of 

 the nephridium, and ends in front by a nephrostome which 

 opens into the next segment. The nephrostome is provided 

 with long ciliated processes. The nephridium of Nereilepas 

 fuc ata is of essentially similar structure. 



